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Acoustic resonance in the potential core of subsonic jets

Towne, Aaron and Cavalieri, André V. G. and Jordan, Peter and Colonius, Tim and Schmidt, Oliver and Jaunet, Vincent and Brès, Guillaume A. (2017) Acoustic resonance in the potential core of subsonic jets. Journal of Fluid Mechanics, 825 . pp. 1113-1152. ISSN 0022-1120. doi:10.1017/jfm.2017.346.

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The purpose of this paper is to characterize and model waves that are observed within the potential core of subsonic jets and relate them to previously observed tones in the near-nozzle region. The waves are detected in data from a large-eddy simulation of a Mach 0.9 isothermal jet and modelled using parallel and weakly non-parallel linear modal analysis of the Euler equations linearized about the turbulent mean flow, as well as simplified models based on a cylindrical vortex sheet and the acoustic modes of a cylindrical soft duct. In addition to the Kelvin–Helmholtz instability waves, three types of waves with negative phase velocities are identified in the potential core: upstream- and downstream-propagating duct-like acoustic modes that experience the shear layer as a pressure-release surface and are therefore radially confined to the potential core, and upstream-propagating acoustic modes that represent a weak coupling between the jet core and the free stream. The slow streamwise contraction of the potential core imposes a frequency-dependent end condition on the waves that is modelled as the turning points of a weakly non-parallel approximation of the waves. These turning points provide a mechanism by which the upstream- and downstream-travelling waves can interact and exchange energy through reflection and transmission processes. Paired with a second end condition provided by the nozzle, this leads to the possibility of resonance in limited frequency bands that are bound by two saddle points in the complex wavenumber plane. The predicted frequencies closely match the observed tones detected outside of the jet. The vortex-sheet model is then used to systematically explore the Mach number and temperature ratio dependence of the phenomenon. For isothermal jets, the model suggests that resonance is likely to occur in a narrow range of Mach number, 0.82 < M < 1.

Item Type:Article
Related URLs:
URLURL TypeDescription
Towne, Aaron0000-0002-7315-5375
Cavalieri, André V. G.0000-0003-4283-0232
Jordan, Peter0000-0001-8576-5587
Colonius, Tim0000-0003-0326-3909
Schmidt, Oliver0000-0002-7097-0235
Brès, Guillaume A.0000-0003-2507-8659
Additional Information:© 2017 Cambridge University Press. Received 12 May 2016; revised 15 February 2017; accepted 18 May 2017; first published online 27 July 2017. A.T. and T.C. gratefully acknowledge support from the Office of Naval Research under contract N0014-11-1-0753. A.V.G.C. and P.J. acknowledge support from the Science Without Borders project no. A073/2013. OTS was supported by DFG grant no. 3114/1-1. The LES study was supported by NAVAIR SBIR project, under the supervision of Dr J. T. Spyropoulos. The main LES calculations were carried out on CRAY XE6 machines at DoD HPC facilities in ERDC DSRC. The authors also thank S. Piantanida and R. Kari for performing the experimental measurements reported in figures 3 and 10.
Funding AgencyGrant Number
Office of Naval Research (ONR)N0014-11-1-0753
Science Without BordersA073/2013
Deutsche Forschungsgemeinschaft (DFG)3114/1-1
Naval Air Systems Command (NAVAIR)UNSPECIFIED
Subject Keywords:absolute/convective instability, acoustics, jets
Record Number:CaltechAUTHORS:20170818-081556658
Persistent URL:
Official Citation:Towne, A., Cavalieri, A., Jordan, P., Colonius, T., Schmidt, O., Jaunet, V., & Brès, G. (2017). Acoustic resonance in the potential core of subsonic jets. Journal of Fluid Mechanics, 825, 1113-1152. doi:10.1017/jfm.2017.346
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:80597
Deposited By: Tony Diaz
Deposited On:18 Aug 2017 17:31
Last Modified:15 Nov 2021 19:37

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